CA1209246A - Dynamic noise filter for an audio signal in a television - Google Patents
Dynamic noise filter for an audio signal in a televisionInfo
- Publication number
- CA1209246A CA1209246A CA000438696A CA438696A CA1209246A CA 1209246 A CA1209246 A CA 1209246A CA 000438696 A CA000438696 A CA 000438696A CA 438696 A CA438696 A CA 438696A CA 1209246 A CA1209246 A CA 1209246A
- Authority
- CA
- Canada
- Prior art keywords
- audio signal
- filter
- signal
- frequency
- frequency range
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/60—Receiver circuitry for the reception of television signals according to analogue transmission standards for the sound signals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/60—Receiver circuitry for the reception of television signals according to analogue transmission standards for the sound signals
- H04N5/607—Receiver circuitry for the reception of television signals according to analogue transmission standards for the sound signals for more than one sound signal, e.g. stereo, multilanguages
Abstract
ABSTRACT
A dynamic noise filter especially adapted for use in audio reproduction systems within a television display device is provided to eliminate perceived noise.
An audio signal having a relatively wide frequency range is passed through a variable bandwidth lowpass filter, the upper frequency cutoff point being variable in response to a control signal. A control path includes a filter and detector circuit for generating the control signal in response to the amplitude of the audio signal within an upper frequency portion of the audio signal frequency range. The control signal controls the bandwidth of the lowpass filter inversely with respect to the level of the audio signal within the upper frequency portion of the frequency range. A further filter is included in the control path for providing substantial attenuation at the fundamental frequency and lower order harmonic frequencies of the television horizontal line scanning signal in order to prevent the control path from erroneously responding to this signal.
A dynamic noise filter especially adapted for use in audio reproduction systems within a television display device is provided to eliminate perceived noise.
An audio signal having a relatively wide frequency range is passed through a variable bandwidth lowpass filter, the upper frequency cutoff point being variable in response to a control signal. A control path includes a filter and detector circuit for generating the control signal in response to the amplitude of the audio signal within an upper frequency portion of the audio signal frequency range. The control signal controls the bandwidth of the lowpass filter inversely with respect to the level of the audio signal within the upper frequency portion of the frequency range. A further filter is included in the control path for providing substantial attenuation at the fundamental frequency and lower order harmonic frequencies of the television horizontal line scanning signal in order to prevent the control path from erroneously responding to this signal.
Description
-1- RCA 78,691 DYNAMIC NOISE FILTER FOR AN
AUDIO SIGNAL IN A TELEVISION
The present invention relates to audio signal processing in a television display device and in particular to a dynamic noise filter arrangement for reducing perceived noise.
It is generally recognized that in an audio signal processing system, system noise can be reduced by rèducing the frequency bandwidth of the system.
Furthermore, a listener's awareness of audio noise can psychoacoustical].y be reduced. That is, the presence of a significant amount of audio signal energy content in the same frequency range as the noise can serve to acoustically "mask" the noise. Dynamic noise filter systems use these two principles for achieving noise reduction.
One t~pe of dynamic noise filter system is used in the LM 1894 integrated circuit which is commercially available from National Semiconductor Corporation, Santa Clara, California and is described in the 1982 National Semiconductor Databook, pages 10-172 to 178 and U.~. Patent 3,678,416. In that system, the upper 3 dB
frequency of a variable bandwidth lowpass filter in a main audio signal path is automatically and continuously controlled in response to the amplitude and frequency content of the audio signal. A parallel connected control signal path includes a highpass filter responsive to the audio signal for applying to a peak detector only the high freguency portion of the audio signal spec-trum. The peak ~ 30 detector generates a control signal which is applied to ;. the variable bandwidth filter of the main signal path. If the energy content of the high frequency portion of the i audio signal is substantial, the control signal causes the - bandwidth of the lowpass filter of the main signal path to increase. In this manner, the high frequency content of the reproduced audio signal is available to "mask" the : system noise and reduce its perception. Conversely, if th~ amount of energy in the high frequency port1on of the ~3~
.. . ..
~2~$~6
AUDIO SIGNAL IN A TELEVISION
The present invention relates to audio signal processing in a television display device and in particular to a dynamic noise filter arrangement for reducing perceived noise.
It is generally recognized that in an audio signal processing system, system noise can be reduced by rèducing the frequency bandwidth of the system.
Furthermore, a listener's awareness of audio noise can psychoacoustical].y be reduced. That is, the presence of a significant amount of audio signal energy content in the same frequency range as the noise can serve to acoustically "mask" the noise. Dynamic noise filter systems use these two principles for achieving noise reduction.
One t~pe of dynamic noise filter system is used in the LM 1894 integrated circuit which is commercially available from National Semiconductor Corporation, Santa Clara, California and is described in the 1982 National Semiconductor Databook, pages 10-172 to 178 and U.~. Patent 3,678,416. In that system, the upper 3 dB
frequency of a variable bandwidth lowpass filter in a main audio signal path is automatically and continuously controlled in response to the amplitude and frequency content of the audio signal. A parallel connected control signal path includes a highpass filter responsive to the audio signal for applying to a peak detector only the high freguency portion of the audio signal spec-trum. The peak ~ 30 detector generates a control signal which is applied to ;. the variable bandwidth filter of the main signal path. If the energy content of the high frequency portion of the i audio signal is substantial, the control signal causes the - bandwidth of the lowpass filter of the main signal path to increase. In this manner, the high frequency content of the reproduced audio signal is available to "mask" the : system noise and reduce its perception. Conversely, if th~ amount of energy in the high frequency port1on of the ~3~
.. . ..
~2~$~6
-2- RCA 78,691 audio signal decreases, the masking ability of khe reproduced audio signal is also decreased. Therefore, as the energy content of the high frequency portion of khe audio signal decreases, the control signal decreases and causes the bandwidth of -the lowpass filter to be reduced.
Consequently, the system bandwid-th is res-trictPd and the noise output is reduced.
When such a system is used for processing a stereophonic audio signal, it is known to include with the highpass filter of the control path an additional filter for preventing the presence of the stereophonic pilot tone signal (e.g., l9 kHz in the United States FM broadcast standard) from being detected and "fooling" the noise reduction system into erroneously increasing the bandwidth of the main signal path. Without a pilot tone filter, the presence of the pilot tone will cause the bandwidth of the lowpass filter to remain wide open irrespective of the amount of energy in the high frequency portion of the audio signal.
It has been suggested that when such a dynamic noise filter as described above is used in a television display device, a control path notch filter similar to the type used for reducing the stereophonic pilot tone signal should be included for reducing the presence of the horizontal line scanning signal (e.g., 15.734 kHz in the NTSC system), in order to prevent the horiæontal line scanning signal from l'fooling" the dynamic noise filter in ~; the same manner as the pilot tone signal in the above described stereophonic audio system.
Although it would seem that such a no-tch circuit tuned to the horizontal line scanning frequency would suffice, i-t is recognized by the present inventor that due to the high amplitude and the non-sinusoidal nature of the line scanning si~nals in the deflection portion of the television display device, this approach is too simplistic. That is, significant amounts of energy exist at the second and third harmonics of the horizontal line scanning frequency, which frequencies are not affected by ,~
.
~Z~ 6
Consequently, the system bandwid-th is res-trictPd and the noise output is reduced.
When such a system is used for processing a stereophonic audio signal, it is known to include with the highpass filter of the control path an additional filter for preventing the presence of the stereophonic pilot tone signal (e.g., l9 kHz in the United States FM broadcast standard) from being detected and "fooling" the noise reduction system into erroneously increasing the bandwidth of the main signal path. Without a pilot tone filter, the presence of the pilot tone will cause the bandwidth of the lowpass filter to remain wide open irrespective of the amount of energy in the high frequency portion of the audio signal.
It has been suggested that when such a dynamic noise filter as described above is used in a television display device, a control path notch filter similar to the type used for reducing the stereophonic pilot tone signal should be included for reducing the presence of the horizontal line scanning signal (e.g., 15.734 kHz in the NTSC system), in order to prevent the horiæontal line scanning signal from l'fooling" the dynamic noise filter in ~; the same manner as the pilot tone signal in the above described stereophonic audio system.
Although it would seem that such a no-tch circuit tuned to the horizontal line scanning frequency would suffice, i-t is recognized by the present inventor that due to the high amplitude and the non-sinusoidal nature of the line scanning si~nals in the deflection portion of the television display device, this approach is too simplistic. That is, significant amounts of energy exist at the second and third harmonics of the horizontal line scanning frequency, which frequencies are not affected by ,~
.
~Z~ 6
-3- RCA 78,691 the notch filter and are able to pass through the highpass filter of the control path relatively unattenuated.
s Therefore, these harmonic signals can "fool" the dynamic noise filter system and severely decrease its 5 effectiveness. It is desirable to provide a dynamic noise filter system which is not easily "fooled" when used in the environment of a television display device.
In accordance with the principles of the present invention a control path filter arrangement for a dynamic 10 noise filter in a television display device has an amplitude versus frequency response characteristic with a substantially bandpass shape, for passing a substantial portion of the high frequency audio signal frequency range while substantially reducing the passage of the television 15 line scan frequency and its lower order harmonic signals.
i Specifically, in a preferred embodiment, the control path filter arrangement includes a series connected capacitor for establishing a highpass amplitude versus frequency characteristic, a notch circuit tuned to the television 20 line scanning frequency for attenuating the horizontal line scanning signal, and a further filter arrangement including a capacitor coupled in shunt at the output of the notch circuit for establishing a lowpass filter amplitude versus frequency characteristic for attenuating 25 the harmonics of the horizontal line scanning frequency and, in combination with the notch filter, also for significantly increasing the attenuation of the horizontal line scanning signal over that produced by the notch filter alone.
-~ 30 In accordance with a further aspect of the invention, a buffer amplifier is coupled between the control path filter arrangement and the detector for providing a substantially constant impedance to the detector, independent of the audio signal fre~uency.
In the drawings:
FIGURE 1 illustrates, partially in block diagram form and partially in schematic diagram form, a television receiver including an audio signal dynamic noise filter . .
.. .
.. . _ , . . . . .
s Therefore, these harmonic signals can "fool" the dynamic noise filter system and severely decrease its 5 effectiveness. It is desirable to provide a dynamic noise filter system which is not easily "fooled" when used in the environment of a television display device.
In accordance with the principles of the present invention a control path filter arrangement for a dynamic 10 noise filter in a television display device has an amplitude versus frequency response characteristic with a substantially bandpass shape, for passing a substantial portion of the high frequency audio signal frequency range while substantially reducing the passage of the television 15 line scan frequency and its lower order harmonic signals.
i Specifically, in a preferred embodiment, the control path filter arrangement includes a series connected capacitor for establishing a highpass amplitude versus frequency characteristic, a notch circuit tuned to the television 20 line scanning frequency for attenuating the horizontal line scanning signal, and a further filter arrangement including a capacitor coupled in shunt at the output of the notch circuit for establishing a lowpass filter amplitude versus frequency characteristic for attenuating 25 the harmonics of the horizontal line scanning frequency and, in combination with the notch filter, also for significantly increasing the attenuation of the horizontal line scanning signal over that produced by the notch filter alone.
-~ 30 In accordance with a further aspect of the invention, a buffer amplifier is coupled between the control path filter arrangement and the detector for providing a substantially constant impedance to the detector, independent of the audio signal fre~uency.
In the drawings:
FIGURE 1 illustrates, partially in block diagram form and partially in schematic diagram form, a television receiver including an audio signal dynamic noise filter . .
.. .
.. . _ , . . . . .
-4- RCA 78,691 constructed in accordance with the principles of the present invention;
FIGURE 2 illustra-tes amplitude versus frequency response curves for the con-trol path filt~r arrangement o~
a dynamic noise filter constructed in accordance with -the prior art and one constructed in accordance with the principles of the present invention; and FIGURE 3 illustra-tes amplitude versus frequency response curves for the main signal path of a dynamic noise filter constructed in accordance with the prior art and one constructed in accordance with the principles of the present invention.
In FIGURE 1, composite color radio frequency (RF) television signals received by an antenna 10 are applied to a tuner 12 which sel~cts the received RF
signals associated with a selected charmel and converts them to intermediate frequency (IF) signals occupying a predesignated range of frequencies. An IF amplification stage 14 includes frequency selective components for ZO applying substantially only the picture IF signal to a video processor 16. Video processor 16 derives a baseband video signal from the picture IF signal and processes the baseband video signal to produce the red (R), green (G) and blue (B) color image representative video signals which are applied to kinescope 18 for reproducing a color image thereon. Additionally, a deflection circuit 2~ is responsive to the baseband video signal fox generating horizontal (H) and vertical (V) synchronizing signals which are applied to the horizontal and vertical deflection coils 22 of kinescope 18 for generating a scanning raster. A sound detector 24 receives the IF
signals from IF amplifier stage 14 and derives a composite audio signal therefrom. Illustratively, the composite audio signal includes an encoded stereophonic signal.
Stereo decoder 26 is responsive to the composite audio signal for supplying at its output left and right stereophonically related audio signals. The left and right audio signals are then processed by a dynamic noise .~
-2~6 I -5- RCA 78,691 filter 28 and applied via audio amplifiers 30 and 32 to speakers 34 and 36 for reproducing the audio information.
Audio amplifiers 30 and 32 preferrably include user adjustable controls for adjusting -the volume and tone of the reproduced audio si.gnals.
Illustratively, dynamic noise ilter 28 is of ~ the aforenoted LM 1894 inteyrated circuit type and 3 includes a left main signal path having a variable bandwidth lowpass filter 38 and a right main signal path having a variable bandwidth lowpass filter 40. Each of lowpass filters 38 and 40 has an upper 3dB corner frequency which is variable between approximately 1 kHz and 30 kHz in response -to an applied control signal. The full bandwidth of the left and right audio signals are applied from decoder 26 to terminals 2 and 13 5the reference numbers of the terminals correspond to the pin designations of the LM 1894) which are in turn coupled to terminals 4 and 11 via lowpass filters 38 and 40, respectively. Lowpass filters 38 and 40 each have a variable single pole lowpass configuration and, may be constructed, e.g., as shown for filter 38 as in the LM1894, using a variable transconductance amplifier 39 driving an operational amplifier integrator 41. Series connected resistors Ri and Rf are formed within the integrated circuit between terminals 2 and 4. The junction between these resistors is connected to the non-inverting input of amplifier 39 for determining the gain of the pass portion of the lowpass characteristic of filter 38. A capacitor CI is connected between terminals 4 and 12 for forming an integrator with amplifier 41.
A control signal path 42 is used for controlling the bandwidth of filters 38 and 40 and includes a highpass filter and a peak detector responsive to the audio signal :~ for generating a control signal Ic which is applied to the ~r 35 variable transconductance amplifiers of lowpass filters 38 and 40 for varying their bandwidth in response to the i amount of high frequency energy within the audio signals.
J' ~
' _ .
2~
-6- RCA 78,691 More specifically, control path 42 includes a summing amplifier 44 connec-ted to terminals 2 and 13 for sampling and combining the left and right audio signals.
A highpass fil-ter arrangement comprised of resistors 46 and 48 and capacitors 50 and 52 is connected between terminals 5 and 6 for passing the high frequency portion of the audio signal spectrum. An amplifier 54 coupled between terminals 6 and 8 provides approximately 26 dB of voltage gain to that portion of the audio signal which passes through the highpass filter arrangement coupled between terminals 5 and 6. A filter 58 including resistor Rl, capacitors C1, C2 and inductor L1 followed by a shunt connected capacitor C3, an isolation or buffer ampliier ~ 60 and a series connected capacitor 62 axe connected ,. 15 between terminal 8 and terminal 9. The purpose of the filter arrangement between terminals 8 and 9 is to reduce the susceptibility of control path 42 from being "fooled"
by undesired signals, and will be discussed in detail further on. The value of capacitor 62 may also be used to help shape -the highpass filter characteristic of control path 42. A peak detector 56 is responsive to the amount of audio signal at terminal 9 for generating the control signal Ic, which is applied to lowpass filters 38 and 40 i for controlling their bandwidth in accordance with the energy content of the high frequency portion of the audio signal.
In operation, the manner in which dynamic noise filter ~8 reduces a listener's awareness of noise is twofold. Firstly, as the energy content in the high frequency portion of the audio signal decreases, the ..
control signal IC generaked by control path 42 decreases s; and the bandwidth of lowpass filters 38 and 40 are ' consequently decreased. Thus, the bandwidth of the main - signal path of the audio reproduction system is also reduced~ It is generally accepted that a reduction in system bandwidth is accompanied by a corresponding reduction in the output noise level. Secondly, when there is substantial energy content in the high frequency i~
, ,.
;246 -7 RCA 78,691 portion of the audio signal, the control signal IC
increases, thus increasing the bandwidth of lowpass filter~ 38 and 40 and allowing them to pass more of the entire spectrum of the audio signal. The presence of the high frequency energy within the reproduced audio reduces perceiYed noise by an auditory "masking" eEfect. That is, whenever one sound is being heard by a listener, it reduces the ability of the listener to hear another sound.
As previously noted, the purpose of notch filter 58 is to prevent control path 42 from being "fooled" by undesired signals. For example, if the audio signal being processed is a stereophonic signal including a pilot tone Ihaving a fre~uency within the audio signal bandwidth (e.g., 19 kHz for United States FM broadcast standards~
the pilot tone will pass through the highpass filter arrangement of control path 42 and undesirably maintain control signal Ic at a high level irrespec-tive of the actual energy content within the high frequency portion of the audio signal. Thus, notch filter 58 can be tuned to provide substantial attenuation at the frequency of the pilot tone signal.
When a noise filter system as described above is used in a television receiver, it is known to tune notch filter 58 for attenuating the amplitude of signals having ~5 the horizontal line scanning fre~uency, which if not attenuated may cause improper operation of the noise filter in the same manner as mentioned above with respect to the pilot tone signal.
It has been recognized however, by the present .~
inventors, that this approach is -too simplistic, due to the high amplitude and non-sinusoidal na-ture of the horizontal line scanning signal developed by the deflection circuitry of the television receiver. Thus, there exists within the television receiver cabinet strong . 35 high fre~uency signals corresponding to the fundamental frequency of the horizontal line scanni.ng signal and several of its lower order harmonics which are radiated `, from, for example, the flyback transformer and are .. . . _ .
~$%46 ~8- RCA 78,691 picked-up by the leads and terminals of the filter arrangements of control path 42. More specifically, the second and third harmonics of the horizontal line scanning signal are particularly troublesome since they fall within
FIGURE 2 illustra-tes amplitude versus frequency response curves for the con-trol path filt~r arrangement o~
a dynamic noise filter constructed in accordance with -the prior art and one constructed in accordance with the principles of the present invention; and FIGURE 3 illustra-tes amplitude versus frequency response curves for the main signal path of a dynamic noise filter constructed in accordance with the prior art and one constructed in accordance with the principles of the present invention.
In FIGURE 1, composite color radio frequency (RF) television signals received by an antenna 10 are applied to a tuner 12 which sel~cts the received RF
signals associated with a selected charmel and converts them to intermediate frequency (IF) signals occupying a predesignated range of frequencies. An IF amplification stage 14 includes frequency selective components for ZO applying substantially only the picture IF signal to a video processor 16. Video processor 16 derives a baseband video signal from the picture IF signal and processes the baseband video signal to produce the red (R), green (G) and blue (B) color image representative video signals which are applied to kinescope 18 for reproducing a color image thereon. Additionally, a deflection circuit 2~ is responsive to the baseband video signal fox generating horizontal (H) and vertical (V) synchronizing signals which are applied to the horizontal and vertical deflection coils 22 of kinescope 18 for generating a scanning raster. A sound detector 24 receives the IF
signals from IF amplifier stage 14 and derives a composite audio signal therefrom. Illustratively, the composite audio signal includes an encoded stereophonic signal.
Stereo decoder 26 is responsive to the composite audio signal for supplying at its output left and right stereophonically related audio signals. The left and right audio signals are then processed by a dynamic noise .~
-2~6 I -5- RCA 78,691 filter 28 and applied via audio amplifiers 30 and 32 to speakers 34 and 36 for reproducing the audio information.
Audio amplifiers 30 and 32 preferrably include user adjustable controls for adjusting -the volume and tone of the reproduced audio si.gnals.
Illustratively, dynamic noise ilter 28 is of ~ the aforenoted LM 1894 inteyrated circuit type and 3 includes a left main signal path having a variable bandwidth lowpass filter 38 and a right main signal path having a variable bandwidth lowpass filter 40. Each of lowpass filters 38 and 40 has an upper 3dB corner frequency which is variable between approximately 1 kHz and 30 kHz in response -to an applied control signal. The full bandwidth of the left and right audio signals are applied from decoder 26 to terminals 2 and 13 5the reference numbers of the terminals correspond to the pin designations of the LM 1894) which are in turn coupled to terminals 4 and 11 via lowpass filters 38 and 40, respectively. Lowpass filters 38 and 40 each have a variable single pole lowpass configuration and, may be constructed, e.g., as shown for filter 38 as in the LM1894, using a variable transconductance amplifier 39 driving an operational amplifier integrator 41. Series connected resistors Ri and Rf are formed within the integrated circuit between terminals 2 and 4. The junction between these resistors is connected to the non-inverting input of amplifier 39 for determining the gain of the pass portion of the lowpass characteristic of filter 38. A capacitor CI is connected between terminals 4 and 12 for forming an integrator with amplifier 41.
A control signal path 42 is used for controlling the bandwidth of filters 38 and 40 and includes a highpass filter and a peak detector responsive to the audio signal :~ for generating a control signal Ic which is applied to the ~r 35 variable transconductance amplifiers of lowpass filters 38 and 40 for varying their bandwidth in response to the i amount of high frequency energy within the audio signals.
J' ~
' _ .
2~
-6- RCA 78,691 More specifically, control path 42 includes a summing amplifier 44 connec-ted to terminals 2 and 13 for sampling and combining the left and right audio signals.
A highpass fil-ter arrangement comprised of resistors 46 and 48 and capacitors 50 and 52 is connected between terminals 5 and 6 for passing the high frequency portion of the audio signal spectrum. An amplifier 54 coupled between terminals 6 and 8 provides approximately 26 dB of voltage gain to that portion of the audio signal which passes through the highpass filter arrangement coupled between terminals 5 and 6. A filter 58 including resistor Rl, capacitors C1, C2 and inductor L1 followed by a shunt connected capacitor C3, an isolation or buffer ampliier ~ 60 and a series connected capacitor 62 axe connected ,. 15 between terminal 8 and terminal 9. The purpose of the filter arrangement between terminals 8 and 9 is to reduce the susceptibility of control path 42 from being "fooled"
by undesired signals, and will be discussed in detail further on. The value of capacitor 62 may also be used to help shape -the highpass filter characteristic of control path 42. A peak detector 56 is responsive to the amount of audio signal at terminal 9 for generating the control signal Ic, which is applied to lowpass filters 38 and 40 i for controlling their bandwidth in accordance with the energy content of the high frequency portion of the audio signal.
In operation, the manner in which dynamic noise filter ~8 reduces a listener's awareness of noise is twofold. Firstly, as the energy content in the high frequency portion of the audio signal decreases, the ..
control signal IC generaked by control path 42 decreases s; and the bandwidth of lowpass filters 38 and 40 are ' consequently decreased. Thus, the bandwidth of the main - signal path of the audio reproduction system is also reduced~ It is generally accepted that a reduction in system bandwidth is accompanied by a corresponding reduction in the output noise level. Secondly, when there is substantial energy content in the high frequency i~
, ,.
;246 -7 RCA 78,691 portion of the audio signal, the control signal IC
increases, thus increasing the bandwidth of lowpass filter~ 38 and 40 and allowing them to pass more of the entire spectrum of the audio signal. The presence of the high frequency energy within the reproduced audio reduces perceiYed noise by an auditory "masking" eEfect. That is, whenever one sound is being heard by a listener, it reduces the ability of the listener to hear another sound.
As previously noted, the purpose of notch filter 58 is to prevent control path 42 from being "fooled" by undesired signals. For example, if the audio signal being processed is a stereophonic signal including a pilot tone Ihaving a fre~uency within the audio signal bandwidth (e.g., 19 kHz for United States FM broadcast standards~
the pilot tone will pass through the highpass filter arrangement of control path 42 and undesirably maintain control signal Ic at a high level irrespec-tive of the actual energy content within the high frequency portion of the audio signal. Thus, notch filter 58 can be tuned to provide substantial attenuation at the frequency of the pilot tone signal.
When a noise filter system as described above is used in a television receiver, it is known to tune notch filter 58 for attenuating the amplitude of signals having ~5 the horizontal line scanning fre~uency, which if not attenuated may cause improper operation of the noise filter in the same manner as mentioned above with respect to the pilot tone signal.
It has been recognized however, by the present .~
inventors, that this approach is -too simplistic, due to the high amplitude and non-sinusoidal na-ture of the horizontal line scanning signal developed by the deflection circuitry of the television receiver. Thus, there exists within the television receiver cabinet strong . 35 high fre~uency signals corresponding to the fundamental frequency of the horizontal line scanni.ng signal and several of its lower order harmonics which are radiated `, from, for example, the flyback transformer and are .. . . _ .
~$%46 ~8- RCA 78,691 picked-up by the leads and terminals of the filter arrangements of control path 42. More specifically, the second and third harmonics of the horizontal line scanning signal are particularly troublesome since they fall within
5 a frequency range which is more easily picked-up and are passed relatively unattenuated by control path 42 ko peak . detector 56.
I In this regard, although notch filter 58 of , control path 42 may be tuned to attenuate the fundamental frequency of the horizontal line scanning signal, the second and third harmonics are relatively unattenuated by the highpass filter characteristic of control path 42.
Thus, in accordance with the principles of the present invention, the highpass filter characteristic of control '. 15 path 42 is modified to provide a substantially bandpass shape for passing relatively unattenuated the upper fre~uency portion of the audio signal spectrum but providing substantial attenuation at the fundamental .j frequency of the horizontal line scan signal and several of its lower order harmonics. Specifically, this is accomplished by the addition of shunt capacitor C3 at the output of notch filter 58. 3uffer amplifier 60 presents a relatively constant impedance to the input of peak detector 56 and provides isolation from the varying output impedance presented by the filter arrangement of control path 42. Additionally, the input impedance of buffer amplifier 60 is selected to provide a desired terminating .. impedance for the filter 58 and capacitor C3 combination.
Furthermore, it may be desirable to include a DC blocking -' 30 capacitor (not shown) serially coupled between amplifiers - 58 and 60 to reduce the curxent drain fxom amplifier 58 due to the terminating impedance presented by buffer amplifier 60.
Capacitor C3 provides a shunt impedance which decreases with increasing re~uency and thus provides a lowpass response characteristic having increasing attenuation within control path 42 for reducing the level of the second and third harmonics of the horizontal line .
2~6 --9~ RCA 78,691 scanning signal. Furthermore, capacitor C3 provides another benefit by significantly increasing the attenuation provided by notch filter 58 at the f-undamenkal frequency of the horizontal line scanning signal. This is 5 accomplished because cclpacitor C3 reduces the impedance which no-tch filter 58 is working in-to, thereby greatly increasing its effectiveness.
Referring to FIGURE 2, wa~eform 201 (dashed line) is a plo-t of the relative amplitude versus freguency 10 response for control path 42 wi-thout capacitor C3 and amplifier 60. Filter 58 is tuned to suppress the fundamental frequency of the horizontal line scan signal (e.g., 15.734 kHz) and provides approximately 22 dB of attenuation at that freguency. Capacitors C1, C2 and 62 15 are responsib~e for providing the substantially highpass shape of response 201. Notch filter 58 is tuned to be resonant at the fundamental frequency SfH) of the horizontal line scanning signal. Above that frequency, however, response 201 is substantially flat and more 20 importantly provides only approximately 8 ds of a-ttenuation at the frequencies of the second and third harmonics (2fH and 3i~) of the horizontal line scanning frec~uency.
Waveform 202 (solid line) shows the relative 25 amplitude versus frequency response for control path ~2 when capacitor C3 and buffer amplifier 60 are included.
At frequencies less than fH, response 202 is substantially bandpass shaped. As compared with waveform 201 for th~
circ-uit without capacitor C3, an additional 21 dB of 30 attenuation is provided at fH. This corresponds to a greater than tenfold increase in attenua-tion produced by control path 42 at this freguency. Furthermore, a greater than fivefold increase in attenuation is provided at 2f~
and 3flH (i.e., an additional 14 dB~. Although one would 35 expect the shunt impedance provided by capaci~or C3 to cause response 202 to have a -6 dB per octave slope with increasing freguency, its attenuation affect on control path a~2 is somewhat compensated for by the corresponding ~ . _ ~Z~ 46 .
-10- RCA 78,691 increase in ability of the series connected c~pacitors of the highpass filter, i.e., capaci-tors 50, 52 and 62, to pass signals as the frequency increases.
FIGURE 3 shows an actual comparison of the deletexious effect upon the abili-ty of the lowpass filters of dynamic noise filter 28 to reduce their bandwidth in the presence of relatively strong interference by the non-sinusoidal horizontal line scanning signal. Response 301 (dashed line) is an attenuation versus ~requency response for lowpass filter 38 when capacitor C3 and buffer amplifier 60 are not included in control path 42, experimentally determined by applying the output signal of an audio signal sweep generator which provides a 0 to 50 kXz frequency sweep at input terminal 2 together with an equal amplitude horizontal line scanning signal obtained by looping a piece of stranded wire around the flyback transformer of the ~elevision recei~er. As clearly shown by response 301, the relatively strong interference signals at fH, 2fH and 3fH are not attenuated enough by 20 control path filter 42 (response 201 of F'IGURE 2) and the dynamic noise filter system erroneously provides a wide bandwidth irrespective of the frequency content of the 4~ audio signal.
~ In contrast, response 302 (solid line) shows the n . 25 response of lowpass filter 38 when capacitor C3 and buffer i amplifier 60 are included in control path 42 under substantially the same experimental conditions noted above ~;
but with notch filter 58 re-tuned to compensate for the effect of added capacitor C3. Note tha-t the significant extra attenuation provided by the modified control path ~2 ~, (response 202 of FIGURE 2) provided enough additional at-tenuation at the fundamental frequencies of the , horizontal line scanning signal and its lower order harmonics to prevent dynamic noise filter 28 from being "fooled" by this strong interfering signal. Although a test of this nature, wherein the interfering signal is of , the same amplitude as the desired audio signal, may seem - extreme, it exemplifies the benefi-ts provided by the .~ .
.~
i. ._ -11- RCA 78,691 improved bandpass characteristic of control path 42. With such an improved control path characteristic grea-ter freedom is achieved for the placement of the audio circuitry within the television receiver resulting in improved packaging densi-ty and lower manufac-turiny cost.
Typical values for the components of the FIGURE
1 embodiment are as follows:
resls-tors capacitors inductors Ri = Rf = 20, ooon CI = .0039~F L1 = 3.3mH
46 48 ' C50= .l~F
Rl = 91Q C52= .OOl~F
Cl = .18~F
C2 = .033~F
C3 = .l~F
C62= 033~F
Buffer amplifier 60 comprises a common emitter amplifier stage having a voltage bias network which presents 330Q as the desired teminating impedance for filter 5B and capacitor C3.
Typical FIGURE 1 component values ~or providing responses 201 of FIGURE 2 and 301 of FIGURE 3 are the same as shown above except R1 = lOOn, C~ F, C2 = .015~F, C~2 = .047~F and L1 = 5.7mH. Note C3 and buffer amplifier 60 are omitted.
Finally, it should be noted that although the sum of resistors 46 and 48 are shown as being equal to lOOOQ, the ratio of their individual resistance values can be varied in order to adjust the signal level provided to detector 56 and thus control -the noise thresh~ld level of ~, 30 dynamic noise filter 28.
. .
~, ;
$
... .
I In this regard, although notch filter 58 of , control path 42 may be tuned to attenuate the fundamental frequency of the horizontal line scanning signal, the second and third harmonics are relatively unattenuated by the highpass filter characteristic of control path 42.
Thus, in accordance with the principles of the present invention, the highpass filter characteristic of control '. 15 path 42 is modified to provide a substantially bandpass shape for passing relatively unattenuated the upper fre~uency portion of the audio signal spectrum but providing substantial attenuation at the fundamental .j frequency of the horizontal line scan signal and several of its lower order harmonics. Specifically, this is accomplished by the addition of shunt capacitor C3 at the output of notch filter 58. 3uffer amplifier 60 presents a relatively constant impedance to the input of peak detector 56 and provides isolation from the varying output impedance presented by the filter arrangement of control path 42. Additionally, the input impedance of buffer amplifier 60 is selected to provide a desired terminating .. impedance for the filter 58 and capacitor C3 combination.
Furthermore, it may be desirable to include a DC blocking -' 30 capacitor (not shown) serially coupled between amplifiers - 58 and 60 to reduce the curxent drain fxom amplifier 58 due to the terminating impedance presented by buffer amplifier 60.
Capacitor C3 provides a shunt impedance which decreases with increasing re~uency and thus provides a lowpass response characteristic having increasing attenuation within control path 42 for reducing the level of the second and third harmonics of the horizontal line .
2~6 --9~ RCA 78,691 scanning signal. Furthermore, capacitor C3 provides another benefit by significantly increasing the attenuation provided by notch filter 58 at the f-undamenkal frequency of the horizontal line scanning signal. This is 5 accomplished because cclpacitor C3 reduces the impedance which no-tch filter 58 is working in-to, thereby greatly increasing its effectiveness.
Referring to FIGURE 2, wa~eform 201 (dashed line) is a plo-t of the relative amplitude versus freguency 10 response for control path 42 wi-thout capacitor C3 and amplifier 60. Filter 58 is tuned to suppress the fundamental frequency of the horizontal line scan signal (e.g., 15.734 kHz) and provides approximately 22 dB of attenuation at that freguency. Capacitors C1, C2 and 62 15 are responsib~e for providing the substantially highpass shape of response 201. Notch filter 58 is tuned to be resonant at the fundamental frequency SfH) of the horizontal line scanning signal. Above that frequency, however, response 201 is substantially flat and more 20 importantly provides only approximately 8 ds of a-ttenuation at the frequencies of the second and third harmonics (2fH and 3i~) of the horizontal line scanning frec~uency.
Waveform 202 (solid line) shows the relative 25 amplitude versus frequency response for control path ~2 when capacitor C3 and buffer amplifier 60 are included.
At frequencies less than fH, response 202 is substantially bandpass shaped. As compared with waveform 201 for th~
circ-uit without capacitor C3, an additional 21 dB of 30 attenuation is provided at fH. This corresponds to a greater than tenfold increase in attenua-tion produced by control path 42 at this freguency. Furthermore, a greater than fivefold increase in attenuation is provided at 2f~
and 3flH (i.e., an additional 14 dB~. Although one would 35 expect the shunt impedance provided by capaci~or C3 to cause response 202 to have a -6 dB per octave slope with increasing freguency, its attenuation affect on control path a~2 is somewhat compensated for by the corresponding ~ . _ ~Z~ 46 .
-10- RCA 78,691 increase in ability of the series connected c~pacitors of the highpass filter, i.e., capaci-tors 50, 52 and 62, to pass signals as the frequency increases.
FIGURE 3 shows an actual comparison of the deletexious effect upon the abili-ty of the lowpass filters of dynamic noise filter 28 to reduce their bandwidth in the presence of relatively strong interference by the non-sinusoidal horizontal line scanning signal. Response 301 (dashed line) is an attenuation versus ~requency response for lowpass filter 38 when capacitor C3 and buffer amplifier 60 are not included in control path 42, experimentally determined by applying the output signal of an audio signal sweep generator which provides a 0 to 50 kXz frequency sweep at input terminal 2 together with an equal amplitude horizontal line scanning signal obtained by looping a piece of stranded wire around the flyback transformer of the ~elevision recei~er. As clearly shown by response 301, the relatively strong interference signals at fH, 2fH and 3fH are not attenuated enough by 20 control path filter 42 (response 201 of F'IGURE 2) and the dynamic noise filter system erroneously provides a wide bandwidth irrespective of the frequency content of the 4~ audio signal.
~ In contrast, response 302 (solid line) shows the n . 25 response of lowpass filter 38 when capacitor C3 and buffer i amplifier 60 are included in control path 42 under substantially the same experimental conditions noted above ~;
but with notch filter 58 re-tuned to compensate for the effect of added capacitor C3. Note tha-t the significant extra attenuation provided by the modified control path ~2 ~, (response 202 of FIGURE 2) provided enough additional at-tenuation at the fundamental frequencies of the , horizontal line scanning signal and its lower order harmonics to prevent dynamic noise filter 28 from being "fooled" by this strong interfering signal. Although a test of this nature, wherein the interfering signal is of , the same amplitude as the desired audio signal, may seem - extreme, it exemplifies the benefi-ts provided by the .~ .
.~
i. ._ -11- RCA 78,691 improved bandpass characteristic of control path 42. With such an improved control path characteristic grea-ter freedom is achieved for the placement of the audio circuitry within the television receiver resulting in improved packaging densi-ty and lower manufac-turiny cost.
Typical values for the components of the FIGURE
1 embodiment are as follows:
resls-tors capacitors inductors Ri = Rf = 20, ooon CI = .0039~F L1 = 3.3mH
46 48 ' C50= .l~F
Rl = 91Q C52= .OOl~F
Cl = .18~F
C2 = .033~F
C3 = .l~F
C62= 033~F
Buffer amplifier 60 comprises a common emitter amplifier stage having a voltage bias network which presents 330Q as the desired teminating impedance for filter 5B and capacitor C3.
Typical FIGURE 1 component values ~or providing responses 201 of FIGURE 2 and 301 of FIGURE 3 are the same as shown above except R1 = lOOn, C~ F, C2 = .015~F, C~2 = .047~F and L1 = 5.7mH. Note C3 and buffer amplifier 60 are omitted.
Finally, it should be noted that although the sum of resistors 46 and 48 are shown as being equal to lOOOQ, the ratio of their individual resistance values can be varied in order to adjust the signal level provided to detector 56 and thus control -the noise thresh~ld level of ~, 30 dynamic noise filter 28.
. .
~, ;
$
... .
Claims (6)
1. A dynamic noise filter for reducing perceived noise in a reproduced audio signal which is processed by an audio signal channel having a relatively wide frequency range in a television display device, said dynamic noise filter comprising:
means, coupled to receive said audio signal, for providing a variable amount of attenuation within an upper frequency portion of said audio signal frequency range, in response to a control signal;
means for generating said control signal in response to the amplitude of said audio signal within said upper frequency portion of said frequency range;
said generating means including a serially coupled filter and signal detector for causing said control signal to control said audio signal attenuation provided by said first mentioned means, in a manner inverse to the amplitude of said audio signal within said upper frequency portion of said frequency range, wherein said filter has an amplitude versus frequency response characteristic of substantially bandpass shape, for passing relatively unattenuated audio signal frequencies within said upper frequency portion of said frequency range which are less than the fundamental frequency of the television horizontal line scanning signal for providing substantial attenuation at frequencies within said frequency range which are greater than said fundamental frequency and include the frequencies of at least some of the lower harmonics of said horizontal line scanning signal.
means, coupled to receive said audio signal, for providing a variable amount of attenuation within an upper frequency portion of said audio signal frequency range, in response to a control signal;
means for generating said control signal in response to the amplitude of said audio signal within said upper frequency portion of said frequency range;
said generating means including a serially coupled filter and signal detector for causing said control signal to control said audio signal attenuation provided by said first mentioned means, in a manner inverse to the amplitude of said audio signal within said upper frequency portion of said frequency range, wherein said filter has an amplitude versus frequency response characteristic of substantially bandpass shape, for passing relatively unattenuated audio signal frequencies within said upper frequency portion of said frequency range which are less than the fundamental frequency of the television horizontal line scanning signal for providing substantial attenuation at frequencies within said frequency range which are greater than said fundamental frequency and include the frequencies of at least some of the lower harmonics of said horizontal line scanning signal.
2. An improved dynamic noise filter for reducing perceived noise in an audio signal which is processed in an audio signal channel having a relatively wide frequency range in a television display device, said dynamic noise filter comprising:
means coupled to receive said audio signal, for providing a relatively constant amount of attenuation to frequencies of said audio signal within a lower frequency portion of said frequency range and providing a variable amount of signal attenuation to said audio signal within an upper frequency portion of said frequency range, said variable amount of attenuation being controlled in response to an applied control signal;
control path filter means coupled to receive said audio signal for generating said control signal in response to the amplitude of said audio signal within said upper frequency portion of said frequency range, said control path filter means including, serially connected, means for forming a highpass filter for passing relatively unattenuated said upper portion of said frequency range, means for providing a notch filter response for attenuating the horizontal line scanning signal of the television display device at its fundamental frequency and a detector for generating said control signal, said variable attenuation means varying said attenuation inversely with respect to the amplitude of said control signal, wherein the improvement comprises:
a further filter means coupled to said notch filter means for providing substantial attenuation at the frequencies of the second and third harmonics of said horizontal line scanning signal and for increasing the attenuation provided by said notch filter means at said fundamental frequency.
means coupled to receive said audio signal, for providing a relatively constant amount of attenuation to frequencies of said audio signal within a lower frequency portion of said frequency range and providing a variable amount of signal attenuation to said audio signal within an upper frequency portion of said frequency range, said variable amount of attenuation being controlled in response to an applied control signal;
control path filter means coupled to receive said audio signal for generating said control signal in response to the amplitude of said audio signal within said upper frequency portion of said frequency range, said control path filter means including, serially connected, means for forming a highpass filter for passing relatively unattenuated said upper portion of said frequency range, means for providing a notch filter response for attenuating the horizontal line scanning signal of the television display device at its fundamental frequency and a detector for generating said control signal, said variable attenuation means varying said attenuation inversely with respect to the amplitude of said control signal, wherein the improvement comprises:
a further filter means coupled to said notch filter means for providing substantial attenuation at the frequencies of the second and third harmonics of said horizontal line scanning signal and for increasing the attenuation provided by said notch filter means at said fundamental frequency.
3. The dynamic noise filter of Claim 2 further including an isolation means coupled between said further filter means and said detector for presenting a substantially constant impedance to said detector independent of said audio signal frequency.
4. The dynamic noise filter of Claim 2 wherein said further filter means comprises a shunt element coupled at the output of said notch filter means.
5. The dynamic noise filter of Claim 4 wherein said highpass filter means comprises a first capacitor, said notch filter means comprises at least a series connected parallel combination of an inductor and a second capacitor and said further filter means comprises a third capacitor coupled in shunt at the output of said notch filter means.
6. The dynamic noise filter of Claim 5 further including an isolation means coupled between said third capacitor and said detector for presenting a substantially constant impedance to said detector independent of said audio signal frequency.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/434,935 US4517602A (en) | 1982-10-18 | 1982-10-18 | Dynamic noise filter for an audio signal in a television |
| US434,935 | 1982-10-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1209246A true CA1209246A (en) | 1986-08-05 |
Family
ID=23726311
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000438696A Expired CA1209246A (en) | 1982-10-18 | 1983-10-11 | Dynamic noise filter for an audio signal in a television |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4517602A (en) |
| JP (1) | JPS5994972A (en) |
| KR (1) | KR910009428B1 (en) |
| CA (1) | CA1209246A (en) |
| DE (1) | DE3337706A1 (en) |
| FR (1) | FR2534761B1 (en) |
| GB (1) | GB2128855B (en) |
| IT (1) | IT1171773B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4761829A (en) * | 1985-11-27 | 1988-08-02 | Motorola Inc. | Adaptive signal strength and/or ambient noise driven audio shaping system |
| US5086474A (en) * | 1990-03-28 | 1992-02-04 | Thomson Consumer Electronics, Inc. | Amplifier having maximum summed power output from a plurality of devices having limited current sinking capability |
| JP4282524B2 (en) * | 2004-03-30 | 2009-06-24 | 三洋電機株式会社 | AM receiver circuit |
| US7587091B2 (en) * | 2004-10-29 | 2009-09-08 | Intel Corporation | De-interlacing using decoder parameters |
| EP1780888A1 (en) * | 2005-10-12 | 2007-05-02 | STMicroelectronics S.r.l. | Notch filter and apparatus for receiving and transmitting radio-frequency signals which comprises said filter |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3543191A (en) * | 1968-06-18 | 1970-11-24 | Warwick Electronics Inc | Controllable filter network |
| US3678416A (en) * | 1971-07-26 | 1972-07-18 | Richard S Burwen | Dynamic noise filter having means for varying cutoff point |
| US4239939A (en) * | 1979-03-09 | 1980-12-16 | Rca Corporation | Stereophonic sound synthesizer |
| US4329714A (en) * | 1980-11-26 | 1982-05-11 | Rca Corporation | Audio distortion eliminator |
-
1982
- 1982-10-18 US US06/434,935 patent/US4517602A/en not_active Expired - Lifetime
-
1983
- 1983-10-11 CA CA000438696A patent/CA1209246A/en not_active Expired
- 1983-10-15 KR KR1019830004876A patent/KR910009428B1/en not_active IP Right Cessation
- 1983-10-17 GB GB08327725A patent/GB2128855B/en not_active Expired
- 1983-10-17 IT IT23337/83A patent/IT1171773B/en active
- 1983-10-17 JP JP58195120A patent/JPS5994972A/en active Granted
- 1983-10-17 DE DE19833337706 patent/DE3337706A1/en active Granted
- 1983-10-18 FR FR8316570A patent/FR2534761B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3337706A1 (en) | 1984-04-19 |
| GB2128855B (en) | 1986-01-29 |
| JPH025074B2 (en) | 1990-01-31 |
| IT8323337A0 (en) | 1983-10-17 |
| KR910009428B1 (en) | 1991-11-15 |
| FR2534761A1 (en) | 1984-04-20 |
| US4517602A (en) | 1985-05-14 |
| GB2128855A (en) | 1984-05-02 |
| KR840006587A (en) | 1984-11-30 |
| DE3337706C2 (en) | 1987-03-19 |
| JPS5994972A (en) | 1984-05-31 |
| FR2534761B1 (en) | 1986-09-19 |
| GB8327725D0 (en) | 1983-11-16 |
| IT1171773B (en) | 1987-06-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4827511A (en) | Automatic gain control circuit for controlling gain of video signal in television receiver | |
| JPH04262682A (en) | Television receiver | |
| US4974087A (en) | Parallel sound if with reference carrier derived from quasi-synchronous video detector | |
| US4577226A (en) | Noise reduction for FM stereophonic systems and particularly useful in television audio systems | |
| CA1209246A (en) | Dynamic noise filter for an audio signal in a television | |
| KR100211413B1 (en) | Fm trap for a television tuner permitting both tv and fm reception through the same tuner | |
| JP2516861B2 (en) | Television receiver | |
| AU638797B2 (en) | Quasi-parallel if with shared saw filter | |
| JP2528291B2 (en) | Video signal processing and display device | |
| CA2065675C (en) | Television receiver with partially by-passed non-linear luminance signal processor | |
| JPH0380364B2 (en) | ||
| JP3344529B2 (en) | Video detection circuit and video signal processing device | |
| JP2895706B2 (en) | Video intermediate frequency circuit | |
| JPH04262684A (en) | Television receiver | |
| CA1151289A (en) | Signal separation networks | |
| JP3607053B2 (en) | Television signal intermediate frequency circuit | |
| CA1266121A (en) | Receiver for sound multiplex broadcast | |
| US5389979A (en) | Chrominance signal playback system and method for video cassette recorders having noise suppression of the chrominance signal | |
| JP2517704B2 (en) | Audio signal receiving device | |
| US3340357A (en) | Television video detector circuit comprising variable load means for controlling frequency response | |
| KR800000317B1 (en) | Automatic luminance channel frequency response control apparatus | |
| US4335470A (en) | Audio de-emphasis circuit | |
| US3562412A (en) | Variable coupling if amplifier including a double-tuned circuit | |
| JPH033015Y2 (en) | ||
| Eilers | NTSC TV receiver performance with upper adjacent channel ATV interference |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |